Tonight we will cross the Antarctic Circle so we can truly say that we have arrived in its waters. The sea temperature is down around +1C, the birdlife has slowly changed and the frequency of bergs has increased – we just know that we are nearing the pack-ice and the great white continent. But what is the Antarctic Circle ? For those that don’t know here is a quick insight:

The world is split into degrees of latitude. Zero degrees is the equator and running parallel to it are increasing degrees as we move towards both Poles which are at 90 degrees. Hence the terms 90 degrees N (North Pole) and 90 degrees S (South Pole).

The earth rotates around the sun in its orbit but the axis of the earth is inclined at approximately 23.5 degrees to its orbit.

The Antarctic Circle is 90 degrees minus the inclination of the earth’s axis (ie 90 minus 23 .5). That puts the Antarctic Circle at approximately 66.5 degrees South.

At the Antarctic Circle on Midsummers Day (21st December) the sun will never set – but it will have the day before and it will do the day after. Conversely on midwinters day ( 21st June) the sun will never rise – but it will have the day before etc.

Once you get south of the Antarctic Circle the number of days when the sun never sets (or never rises in winter) will increase towards the Pole where an amazing event occurs. Here the summer is 6 months long – when the sun never sets – and the winter is 6 months long – when the sun never rises. That means that at the South Pole the sun only rises once a year and conversely sets once a year. This rising and setting occurs on the spring and autumn equinox which is determined by the sun crossing over the earth’s equator as the earth orbits the sun. In reality this fact is slightly incorrect as the South Pole is at a height of 2835 metres and atmospheric distortion may also play its part in giving them a few more days of sunlight.

If anyone is interested in learning about such things I can highly recommend a great app “SolarWalk” which, for a couple of pounds, has a huge amount of interest. Other apps are available and I can guarantee no personal financial interest in this product etc, etc.

We will be on the ice very soon now and heading towards that winter darkness. We need to be ready.